Purification of strontium



May 3 i945. P'. P. ALEXANDER PURIFICATION 0F STRONTIUM riginal Filed March 5, 1943 M ATTORNFVS Patented ay 8, i945 Aras:y ATENr ruamoa'rron or s'rRoN'rIUM.

Peter P. Alexander, Marblehead, Mass., assignor to Metal Hydrdes Incorporated, Beverly, Mass., a corporation of Massachusetts Original application March 5, 1943, Serial No.

Divided and this application April 26, 1944, Serial No.l 532,737

20 Claims.

This invention relates to the purification of strontium contaminatedwith metal impurities having a lower boiling point, and has for its'object more particularly certain improvements-rin the method of purifying strontium contaminated with alkali metal impurities, such as sodium and potassium.

strontium metal is usually made bysubject` ing fused strontium chloride to electrolysis. Since the salts 'of the alkali metals, sodium and potassium, are usually present in the-strontium chloride, the resulting strontium metal is usually contaminated with a small amount of alkali metal, as Well as of the strontium chloride itself.

To purify the strontium metal, it has been proposed to subject it to distillation in a closed retort that has been evacuated to remove objectionable air. The distilled strontium is permitted to condense in a cooler part of the retort, usually in the form of a more or less spongy deposit;

-while the alkali metal impurities condense in a still cooler part of the retort. After cooling the retort, air is admitted, the retort is opened and the condensed strontium is removed. The resulting product is so reactive that it frequently oxidizes rapidly on the surface and produces heat in suflicient amount -to ignite the whole'mass,

' with the result that fires arequite common. This objectionable result is all the more apt to occur because of the presence of the more highly reactive sodium and potassium. The small deposits of sodium and potassium are so reactive that they almost invariably catch re when the `retort is opened and they come in contact with'the oxygen of air.

As a result of my investigations, I have discovered that these disadvantages may be overcome for the most part, The alkali metals, sodium and potassium, may be segregated from the strontium metal in a form to make them non-in- Y 'Fig 2 is a horizontal section on the line 2-2 flammable on exposure to the oxidizing inuence of air. The strontium metal may be separately collected and it mayat the same time be substantially freed of its chloride.

In accordance with the invention, the strontium metal is heated in lthe absence ci air to a temperature sufciently high to distill the alkali metal impurity or impurities.v The alkali metal vapor is selectively oxidized by bringing it in reactive contact with a. refractory oxide, such as titanium oxide, zirconium oxide and chromium oxide, and the resulting oxidized alkali metal impurity is collected as a solid separate from the strontium metal to be purified. kThestrontium metal itself is advantageously distilled and con- .The apparatus shown comprises an outer retort It" supported within a heating furnace Il, the

retort being held in position by means of two ormore supports I2 resting on top of the heating furnace. The retort preferably consists of heatresistant steel. It is provided witha removable cover l3.having attached thereto a vertical pipev lli and lateral vvalved branches I5 and It, connectable with a. source of vacuum, and air, respectively. A removable inner retort 20, having an open top, rests within the outer retort. A removable tray 2| rests over the open top of the retort, being supported thereon by means of three or more lugs 22 extending over the wall of the inner retort. The heating furnace Il consists essentially of a rectangular chamber 23 having a refractory bottom 2li, side and end walls 25, and

a top 26 having an opening of a size adapted to receive the outerretort. An expanding opening 2l isprovided at or near a lower corner of one of the side walls 0f the chamber, for the introduction of heating gases into the chamber. A similar opening 28 is preferably provided at or near an opposite corner, as a spare or auxiliary means for introducing heating, or cooling, gases into the chamber. When -not in'use, the opening 28 is-closed. A ue opening 29 extends through the same wall as the opening' 2l, preferably at a higher level, so that heating gases passed into the chamber through the opening 21 tend to pass around the retort before leaving the chamber through the flue opening 29.

The apparatus may be used as follows: A charge of strontium, for example, contaminated with sodium, potassium, and strontium chloride, is placed in the bottom of the inner retort 20. The

'inner retort is, then placed in the outer retort I0.

A layer of titanium oxide 3l) is placed in the tray 2|., which is in turn placed across the open top' I of theinner retort. The removable cover i3 is placed on the outer retort I0 and locked thereon to provide a sealed joint. The lateral branch l5 is then connected to a source of vacuum. With A the valveof lateral branch open, and the valve of the other lateral branch i6 closed,. the outer and inner -retorts are placed under vacuum to remove objectionable air.

Heating gases are passed through opening 2l 4into' the heating chamber, where they circulate almost completely around the retort and then pass through the flue opening 28 to the outside atmosphere. lAs the lower` portion of the outer retort lil is heated, the lower portion of the inner retort 2U is also heated. As the temperature rises, a point is reached where the sodium and potassium present in the strontium are distilled. The resulting sodium and potassium vapors rise to the upper and cooler portion of the retort where they come in contact with the titanium oxide 3l! in the tray 2l. Due to their great ailinity for oxygen, the sodium and potassium are promptly oxidized and the titanium dioxide is reduced to titanium and a sub-oxide of titanium, according to reactions which may be indicated as follows:

Na-l-TiOzr-NaOM-'Ii Na+4'Ii02- Na02+2TinOs K+'IiOz KOz+Ti I K|4Ti0z KOc+2Tia0s As the temperature at the bottom of the inner retort continues to rise, a point is reached where the strontium is distilled and its resulting vapor ltends to condense and settle out against the wall of the inner retort immediately below the tray I. Some strontium vapor may of course rise sufficiently to come in contact with titanium dioxide in the tray and react with it in a manner similar tosodium Aor potassium vapor. The bulk of the distilled strontium may, however, be separately condensed and collected, as shown.' A residue consisting essentially of strontium chloride, admlxed perhaps with a small amount of sodium chloride or potassium chloride, or both, remains 'as' a residue in the bottom of the inner retort# i points, their vapors cene selectively to rise highest in the retort. Since the strontium has the Y higher boiling point, its vapor tends not to rise The introduction of heating gases tothe heating chamberis stopped. and the retort is permitted to cool. The cooling operation may be accelerated by be cooling air through the heatine c, for example, through the open-- ing 2C, or lay-removing the outer retortand its contente' 'from the heating chamber. `After the retort hasbeen suitably cooled, lateral branch it is opened to admit air tothe interior or the re- -vtorts, after which the cover i3 is removed. The inner retort and tray are pulled out of the outer retort; the tray is removed, and the condensed strontium is scraped on and separately recovered. The residues are' advantageously removed by g the inner retort with water.

it wuibecleer tomos@ snnedlnthis munt the invention' lends itself to numerous modifications. Instead or titanium oxide, other suitable metallic oxides, such as zirconium oxide 'and orlde, may `he employed, either separately or aldmixeei.`

In the practice or the invention, advantage is tekenof the relative boiling points ol' thometals.-

pointso! sodium and potassium are mommy below `can; o: ummm. 'me seme peruture-otthe montium is, therefore. gradually elevated to a point -where the alkali metal iin-,- plllilzyo'f lower boiling point isi-distilled. Byhetitc-lbottom, the vretort is` caused to yieldl a ranno.` being hottest Vat itsbotbomjndcooieetetlts top. Bincctheso-v diam and potassium have the lower bollino 1s' compounds in accordance with the present invention.

This application is a division oi my co-pending application Serial No. 478,095, tiled March 5, lil/i3.

l' claim:

l. In the method of purifying strontium contaminated with an alkali metal impurity, the improvement which comprises heating the stron- -tium in .the absence of air to a temperature at which the alkali metal impurity but not the strontium is distilled, selectively oxidizing the re sulting alkali metal impurity vapor in a zone removed from the main body of strontium'to be purified, and collecting the oxidized alkali metal 4impurity as a solid separate from the strontium to be puriiied.

2. Method according to claim 1, in which the resulting vapor of the alkali metal impurity is selectively oxidized by bringing it into reactive contact with a refractory metal oxide in a zone removed from the main' body oi strontium to be purled.

3. Method according to claim 1, in which theA resulting vapor ofthe alkali metal impurity la selectively' oxidized 'by bringing it into reactive .contact with titanium oxide-in a zone removed from the main body or strontium to be purined.

-4. Method according to claim 1, in which the resulting vapor or the alkali metal impurity is selectively oxidized by brlngln it into reactive contact with zirconium oxide in a zone removed from the main body` of strontium to loe puriged.

5. vltticthod according to claim 1, in which the resulting vapor of the alkali metal impurity is v selectively oxidized by bringing it into reactive contact with chromium oxide in a zone removed fron the main body of strontium to be purie 6. Method according to claim l, in which the strontium to be purined is also distilled, and condensing` the resulting strontium vapor as a solid separate from theoxidized alkali metal impurity in a zone intermediate that in which the alkali metal impurity is oxidized and that from. which the main body of strontium is distilled."

, '1. In a method of purifying strontium contaminated with sodium as an impurity, the improvement which comprises heating the strontium in the absence of slr to a temperature suillciently high to distill the sodium but4 not the strontium, selectively oxidizing the resulting sodium vapor in a zone removed from the main body of strontium to be purliled, and collecting the oxidized sodium as a solid separate i'rom the strontium. Y

8. Method according to claim 7, in which the resulting sodium vapor is selectively oxidized by bringing it into reactive contact witha reae'aaoi by bringing it into reactive contact with fractory metal omde in a zone removed from the main body of strontium to be puried.

9. Method according to claim 7, m which the resulting sodium vapor is selectively oxidized by bringing it into reactive contact with tita-y nium oxide in a zone removed from the main body of strontium to be puried.

10. Method according to claim 7, in which the i resulting sodium vapor is selectively oxidized by bringing it into reactive contact with zirconium omde in a zone removed from the main body of strontiumto be puried.

11. Method` according to claim '7, in which the resulting sodium vapor is selectively oxidized by bringing it into reactive contact with chromium oxide in a zone removed from the main body of strontium to be purified.

12. Method according to claim 7, in which the strontium to be purified is also distilled, and condensing the resulting strontium vapor as a. solid separate from'the oxidized sodium impurity in a zone intermediate that in which the sodium impurity is oxidized and that from which the main body of strontium is distilled. v

13. In the method of purifying strontiumcontaminated with potassium as an impurity, the v improvement which 4comprises heating the strontium in the absence of air to a temperature sumciently high to distill the potassium but not the strontium, selectively oxidizing the 'resulting potassium vapor in a zone removed from the main body of strontium to be puried, and collecting` the .oxidized potassium as a solid separate from the strontium.

14.'Method according to claim 13, in which the resulting potassium vapor is selectively oxidized by bringing it into reactive contact with a refractory metal oxide in a zone removed from the main body of strontium to lbe puried.

15. Method according to claim13, in which the resulting potassium vapor is selectively oxidized by bringing it' into reactive contact with tita. nium oxide in a zone removed from the main body of strontium to be puried.

16. Method according to claim 13, in which th puried, collecting the oxidized sodium as, a

solid separate from the strontium, distilling the sium impurity is oxidized and that-from whichthe main -body of strontium is distilled.

19. In the method of purifyingstrontium con-- taminated with an alkali metal impurity, the improvement which comprises heating the strontium inthe absence of air to a temperature at' .which the alkali metal impurity but not the strontium is distilled, selectively oxidizing the resulting alkali metal impurity vapor by bring ing it into reactive contact with a refractory -metaloxide in a zone removed from the, main body of strontium to be puried, and collecting the oxidized alkali metal impurity as a solid separate from the strontiumfto be purified. l

20. In the method of purifying strontium con-y taminatedwithl sodium as an impurity. the improvement'which comprises heating the strontium in the absence of air to a temperature sumciently high to distill the'sodiuml but not the strontium,A selectively oxidizing the resulting sodium vapor by bringing it into reactive con-'V tact with a refractory metal oxide ina zone removed from the main body of strontium tobe strontium, and condensing the resulting strondit tium vapor as a solid'separate from the oxidized resulting potassium vapor is selectively oxidized sodium impuritiy in a zone intermediate that in which the sodium impurity is oxidized and that' disfrom which the main body of strontium is tilled. A

' PETER P. 

